Destruction of articular cartilage is the hallmark of inflammatory arthritides. Enzymes elaborated by mononuclear cells infiltrating the synovium mediate, in part, the degradation of the cartilage extracellular matrix. Since mononuclear cells are the dominant cell type found in chronic inflammatory synovitis, we investigated whether interaction of immune mononuclear cells with antigen initiated the synthesis and secretion of a proteoglycan-degrading enzyme activity. Proteoglycan-degrading enzyme activity was monitored by the capacity of murine spleen cell conditioned medium to release [3H]serine/35SO4 incorporated into rabbit cartilage proteoglycan monomer fraction (A1D1), and by the relative change in specific viscosity of bovine nasal cartilage proteoglycan monomer. The results demonstrated that both virgin and immune mononuclear cells spontaneously generated proteoglycan-degrading enzyme activity and that cellular activation and proliferation induced by the antigen keyhole limpet hemocyanin or the mitogen phytohemagglutinin was not required. Kinetic studies demonstrated stable release of the enzyme activity over 72 h. Cell separation studies showed that T lymphocytes, a thymoma line, and macrophages separately produced proteoglycan-degrading enzyme activity. The enzyme activity has been partially characterized and appears to belong to a class of neutral pH metal-dependent proteinases. These observations, the first to demonstrate that T lymphocytes secrete an enzyme zJournal of Clinical Investigation -- Secretion of an articular cartilage proteoglycan-degrading enzyme activity by murine T lymphocytes in vitro. Se Degradinggorgeousunclothedteachers Lv V 1KKAQN4V Degrading Gorgeous Unclothed Teachersm Degrading Gorgeous Degrading Teachers fJournal of Clinical Investigation -- Secretion of an articular cartilage proteoglycan-degrading enzyme activity by murine T lymphocytes in vitro. Se Degradinggorgeousunclothedteachers Lv V 1KKAQN4V Degrading Gorgeous Unclothed Teacherse q o o Teachers Degrading Unclothed